Re: [PATCH v2] rust: build: remap path to avoid absolute path

[Nicolas Schier <nsc@kernel.org>]

On Thu, Feb 26, 2026 at 03:21:11PM +0000, Gary Guo wrote:
> From: Gary Guo <gary@garyguo.net>
> 
> When building with a out directory (O=), absolute paths can end up in the
> file name in `#[track_caller]` or the panic message. This is not desirable
> as this leaks the exact path being used to build the kernel and means that
> the same location can appear in two forms (relative or absolute).
> 
> This is reported by Asahi [1] and is being workaround in [2] previously to
> force everything to be absolute path. Using absolute path for everything
> sovles the inconsistency, however it does not address the reproducibility
> issue. So, fix this by remap all absolute paths to srctree to relative path
> instead.
> 
> This is previously attemped in commit dbdffaf50ff9 ("kbuild, rust: use
> -fremap-path-prefix to make paths relative") but that was reverted as
> remapping debug info causes some tool (e.g. objdump) to be unable to find
> sources. Therefore, use `--remap-path-scope` to only remap macros but leave
> debuginfo untouched. `--remap-path-scope` is only stable in Rust 1.95, so
> use `rustc-option` to detect its presence. This feature has been available
> as  `-Zremap-path-scope` for all versions that we support; hwoever due to
> bugs in the Rust compiler, it does not work reliably until 1.94. I opted to
> not enable it for 1.94 as it's just a single version that we missed.
> 
> This change can be validated by building a kernel with O=, strip debug info
> on vmlinux, and then check if the absolute path exists in `strings
> vmlinux`, e.g. `strings vmlinux |grep \/home`.
> 
> Reported-by: Janne Grunau <j@jannau.net>
> Reported-by: Asahi Lina <lina+kernel@asahilina.net>
> Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Per-call-site.20data.20and.20lock.20class.20keys/near/572466559 [1]
> Link: https://github.com/AsahiLinux/linux/commit/54ab88878869036c9d6620101bfe17a81e88c2f9 [2]
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
> Changes since v1:
> - Restrict remap scope to macro only
> - Add to RUSTFLAGS instead of adding directly to scripts/Makefile.build
> ---
>  Makefile      | 3 +++
>  rust/Makefile | 5 +++--
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 

Acked-by: Nicolas Schier <nsc@kernel.org> # kbuild